Gila River - Geography

Geography

The Gila River has its source in western New Mexico, in Sierra County on the western slopes of Continental Divide in the Black Range. It flows southwest through the Gila National Forest and the Gila Cliff Dwellings National Monument, then westward into Arizona, past the town of Safford. After flowing along the southern slope of the Gila Mountains in Graham County through a series of canyons, the Gila is impounded by Coolidge Dam in San Carlos Lake south of Peridot.

It emerges from the mountains into the valley southeast of Phoenix, Arizona, where it crosses the Gila River Indian Reservation as an intermittent stream due to large irrigation diversions. Well west of Phoenix, the river bends sharply southward along the Gila Bend Mountains, then it swings westward again near the town of Gila Bend. It flows southwestward through the Gila Mountains in Yuma County, and finally it empties into the Colorado at Yuma, Arizona.

The Gila is joined by many tributaries, beginning with the East and West Forks of the river, which combine to form the main stem near Gila Hot Springs in New Mexico. Above Safford, it is joined by the San Francisco River and the intermittent San Simon River. Further downstream it is joined by the San Carlos River from the north in San Carlos Lake. At Winkelman, Arizona it picks up the San Pedro River and then is joined by the Santa Cruz River south of Casa Grande. The Salt River, its main tributary, joins in the Phoenix metro area, and further west the Gila receives its last two major tributaries, the Agua Fria and Hassayampa Rivers, from the north.

Although the Gila River flows entirely within the United States, the headwaters of two tributaries – the San Pedro and Santa Cruz Rivers – extend into Mexico. About 1,630 sq mi (4,200 km2), or 2.8% of the Gila's 58,200-square-mile (151,000 km2) watershed, is in Mexico. A further 3,300 sq mi (8,500 km2) or 5.7% lies within New Mexico, while the remaining majority, 53,270 sq mi (138,000 km2) or 91.5%, is in Arizona.